Fluorescent substance containing nitrogen, method for manufacturing the same, and light-emitting device

ABSTRACT

Disclosed is a method for manufacturing a nitrogen-containing fluorescent substance comprising accommodating an oxide fluorescent substance containing two or more elements in a receptacle made of a material containing carbon, and sintering the oxide fluorescent substance in a mixed gas atmosphere containing nitrogen gas.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2004-207723, filed Jul. 14, 2004,the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method for manufacturing a fluorescentsubstance containing nitrogen, to a fluorescent substance containingnitrogen, and to a light-emitting device employing the fluorescentsubstance containing nitrogen.

2. Description of the Related Art

Nowadays, there is an increasing trend to employ a white light-emittingdiode (white LED) in various fields. The white LED emits white light insuch a manner, for example, that several kinds of light to be emittedfrom several kinds of fluorescent substances each employed for shiftingthe wavelength of part of light emitted from an LED chip are mixed withthe light that has been emitted from an LED chip without the wavelengththereof being shifted at all so as to obtain white light. In theconventional white LED however, since it is difficult to obtain thelight of long wavelength side in the visible radiation region, the lightemitted from the conventional white LED becomes somewhat yellowishwhite. Because of this, this white light is insufficient in color toneif it is to be employed as an illumination for display application orfor medical application, so that there is a strong demand for an LEDwhich is capable of emitting a somewhat reddish white light.

As for the fluorescent substance which is capable of emitting a reddishlight when an ultraviolet or blue light-emitting diode is employed as alight source, there has been proposed a nitride fluorescent substancehaving a composition represented by M_(X)Si_(Y)N_(Z):Eu (wherein M is atleast one selected from the group consisting of Ca, Sr, Ba and Zn;Z=(⅔)X+( 4/3)Y; preferably X=2 and Y=5 or X=1 and Y=7). Since thisfluorescent substance is capable of absorbing light having a shortwavelength ranging from 300 to 550 nm and capable of emitting a lighthaving a long wavelength ranging from 550 to 750 nm, it is possible,through the employment of this fluorescent substance, to emit lightsranging from yellow to red from the light of ultraviolet region whileabsorbing visible lights of indigo, blue and bluish green.

The aforementioned nitride fluorescent substance can be manufactured insuch a manner that a base material of fluorescent substance, and arefined metal or a nitride thereof acting as an activator are mixedtogether and then subjected to sintering in an ammonia atmosphere usinga boron nitride crucible at a temperature ranging from 1200 to 1600° C.In this case, since an apparatus for disposing ammonia employed as anatmospheric gas is required to be installed and moreover, since theprocess is complicated and a manufacturing apparatus of large scale isrequired to be employed, the cost for manufacturing the nitridefluorescent substance would become high. Furthermore, if an LED which iscapable of emitting white light is to be manufactured by using thisnitride fluorescent substance, another fluorescent substance which iscapable of emitting yellow light or blue light is required to beemployed in combination with this nitride fluorescent substance.

As described above, the conventional nitride fluorescent substance isaccompanied with problems that it is difficult to manufacture afluorescent substance exhibiting useful light-emitting properties andthat it is difficult to determine a suitable mixing ratio for theadjustment of white-emitting light.

BRIEF SUMMARY OF THE INVENTION

A method for manufacturing a nitrogen-containing fluorescent substanceaccording to one aspect of the present invention comprises accommodatingan oxide fluorescent substance containing two or more metal elements ina receptacle made of a material containing carbon; and sintering theoxide fluorescent substance in a mixed gas atmosphere containingnitrogen gas.

A method for manufacturing a nitrogen-containing fluorescent substanceaccording to another aspect of the present invention comprises sinteringan oxide fluorescent substance represented by the following generalformula (1) in a mixed gas atmosphere containing nitrogen gas, therebyconverting at least part of the oxide fluorescent substance into anitrogen-containing fluorescent substance represented by the followinggeneral formula (2):

M₂SiO₄:Z  (1)

M₂Si₅N₈:Z  (2)

(wherein M is at least selected from the group consisting of Sr, Ba andCa; and Z is at least of activator selected from the group consisting ofEu and Ce).

A nitrogen-containing fluorescent substance according to one aspect ofthe present invention comprises which is manufactured by theaforementioned methods.

A light-emitting device according to one aspect of the present inventioncomprises a light-emitting element having a first emission spectrum; anda fluorescent layer comprising a nitrogen-containing fluorescentsubstance which is manufactured by the aforementioned methods, thenitrogen-containing fluorescent substance shifting the wavelength of atleast part of the first emission spectrum, thereby exhibiting a secondemission spectrum formed of at least one emission band and fallingwithin a different wavelength region from that of the first emissionspectrum.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a cross-sectional view illustrating the construction of thelight-emitting device according to one embodiment of the presentinvention;

FIG. 2 is a graph showing an emission spectrum obtained from theexcitation of near-ultraviolet-LED by the fluorescent substance ofExample 3;

FIG. 3 is a graph showing an emission spectrum obtained from theexcitation of blue-LED by the fluorescent substance of Example 3;

FIG. 4 is a graph showing an emission spectrum obtained from theexcitation of near-ultraviolet-LED by the fluorescent substance ofExample 7;

FIG. 5 is a graph showing an emission spectrum obtained from theexcitation of blue-LED by the fluorescent substance of Example 7;

FIG. 6 is a graph showing an excitation spectrum of the fluorescentsubstance of Example 7; and

FIG. 7 is a graph showing an emission spectrum obtained from theexcitation of near-ultraviolet-LED by the fluorescent substance ofExample 8.

DETAILED DESCRIPTION OF THE INVENTION

Next, the embodiments of the present invention will be explained.

In the method for manufacturing a fluorescent substance according to oneembodiment of the present invention, an oxide fluorescent substance isemployed as a raw material. Preferably, the oxide fluorescent substanceuseful in this case comprises two or more metal elements, exhibiting anemission spectrum falling within a region ranging from blue to orangecolor. This oxide fluorescent substance has a composition represented bythe following general formula (1):

M₂SiO₄:Z  (1)

(wherein M is at least one selected from the group consisting of Sr, Baand Ca; and Z is at least one activator selected from the groupconsisting of Eu and Ce).

A nitride fluorescent substance can be obtained by thereduction/nitrification of the aforementioned oxide fluorescentsubstance, the nitride fluorescent substance thus manufactured beingenabled to emit light from the entire body thereof. It is possible,through the control of nitrification of the oxide fluorescent substanceemployed as a raw material, to obtain a mixed fluorescent substancecomprising of a nitride fluorescent substance and a raw oxidefluorescent substance, thus making it possible to manufacture a mixedfluorescent substance comprising an optional ratio of a nitridefluorescent substance and a raw oxide fluorescent substance, which issuitable for coating on a near-ultraviolet or blue light-emitting diode.The composition ratio ((the weight of a nitride fluorescentsubstance)/(the weight of an oxide fluorescent substance)) in the mixedfluorescent substance can be varied by changing, for example, thesintering atmosphere (the concentration of hydrogen, etc.) and thesintering conditions (such as temperature and time). For example, whenthe concentration of hydrogen in the atmosphere is increased, theaforementioned composition ratio would become higher. Further, when thesintering temperature is made higher or when the sintering time is madelonger, the aforementioned composition ratio can be increased.

Alternatively, it is also possible to control the aforementionedcomposition ratio in the mixed fluorescent substance by treatments aftersintering. More specifically, by dipping a fluorescent substance in anaqueous solution of a strong acid such as hydrochloric acid, nitricacid, sulfuric acid, etc. subsequent to the aforementioned sintering, itis possible to vary the aforementioned composition ratio. For example,when the concentration of the aforementioned acids is increased to pH=1or when the dipping time is prolonged by about one hour, the weight ofthe oxide fluorescent substance can be decreased, thus increasing theaforementioned composition ratio in the mixed fluorescent substance.

In this specification, the term “nitrogen-containing fluorescentsubstance” is intended to include not only a nitride fluorescentsubstance but also a mixed fluorescent substance comprising a nitridefluorescent substance and a raw oxide fluorescent substance.

The oxide fluorescent substance to be employed as a raw material shouldpreferably be a high luminance oxide fluorescent substance where thelight-emitting characteristics thereof are adjusted in advance. Because,in the case where a mixed fluorescent substance is to be manufacturedthrough the reduction/nitrification of part of an oxide fluorescentsubstance of high luminance, the high luminance thereof wouldmaintained, thus making the resultant mixed fluorescent substance alsohigh in luminance.

The oxide fluorescent substance can be synthesized according to anyconventional method. For example, a raw material powder constituting theM component in the above formula (1), SiO₂ powder and Eu₂O₃ powder aremixed together at first. As for the raw material powder constituting theM component, it is possible to employ SrCO₃, BaCO₃, CaCO₃, etc. Althoughthere is not any particular limitation with respect to the averageparticle diameter of these powders, it is preferable to confine theaverage particle diameter of these powders within the range of 0.1 to 10μm in order to enable the solid reaction of these powders to proceeduniformly and sufficiently. The mixture thus obtained is then subjectedto sintering in a reducing nitrogen/hydrogen atmosphere at a temperatureranging from 1000 to 1400° C. In this case, the sintering may beperformed by using a sintering assistant such as ammonium chloride, etc.After finishing the sintering, the oxide fluorescent substance ispulverized by ball mill and then washed with water. Thereafter, thepulverized particles are sieved to obtain the oxide fluorescentsubstance having particle diameters ranging from 5 to 20 μm, which isthen allowed to dry by drying oven. By going through these steps, anoxide fluorescent substance to be employed as a starting material can beobtained. However, an oxide fluorescent substance which is available inthe market may be employed.

The oxide fluorescent substance is accommodated in a receptacle forperforming the sintering of the oxide fluorescent substance. Herein,with respect to the features of the receptacle, there is no particularlimitation as long as it is capable of accommodating the oxidefluorescent substance and hence it is possible to employ, apart from aso-called crucible, receptacles of various configurations such as aplate-like configuration, a rod-like configuration, etc.

Since a receptacle made of a carbon-containing material does notobstruct the reaction system, it is possible to obtain a fluorescentsubstance which is high in purity and excellent in emissioncharacteristics. Specific examples of such a receptacle include thoseformed of carbon or silicon carbide (SiC). The receptacle may be alsoformed of a mixture of carbon and silicon carbide. It has beenconfirmed, as a result of studies made by the present inventors, thatalumina (Al₂O₃), boron nitride (BN) and quartz are unsuitable for use asa material for the receptacle to be employed herein due to the followingreasons. Namely, alumina (Al₂O₃) is unsuitable since it obstructs thenitriding reaction or the reaction system, boron nitride (BN) isunsuitable for use as a material for the receptacle to be employed isnot suited for use since it will be decomposed in a nitrogen/hydrogenatmosphere, and quartz is not suited for use since a receptacle made ofquartz would melt at the sintering temperature. It is now possible,through the employment of a receptacle made of carbon or siliconcarbide, to reduce and nitrize an oxide fluorescent substance, therebyobtaining a desirable nitride fluorescent substance.

The receptacle having an oxide fluorescent substance positioned thereinis subjected to sintering in a reducing mixed gas atmosphere containingnitrogen gas. This reducing mixed gas atmosphere containing nitrogen gascan be prepared by using a mixture comprising hydrogen gas and nitrogengas. The mixing ratio between hydrogen gas and nitrogen gas (H₂:N₂) maybe about 10:90-70:30 (volume ratio). If the content of hydrogen gas islower than this lower limit, the reduction of the oxide would becomeinsufficient. On the other hand, if the content of nitrogen gas is lowerthan this lower limit, it may become impossible to obtain a desiredquantity of nitrogen-containing fluorescent substance.

The reduction/nitrification of the oxide fluorescent substance can beachieved by sintering the oxide fluorescent substance at a temperatureof, for example, 1600° C. or more. In this sintering, it is possible toemploy a tube furnace, a compact furnace or a high-frequency furnace.The sintering temperature should preferably be confined within the rangeof 1600 to 1700° C. Preferably, the sintering should be performed in asingle sintering step wherein the sintering is performed for 2 to 10hours at a temperature of 1600° C. or more. However, the sintering maybe performed in a two-step sintering wherein the first sintering step isperformed for 1 to 3 hours at a temperature ranging from 800 to 1400° C.and the second sintering step is performed for 1 to 9 hours at atemperature of 1600° C. or more.

By going through the aforementioned process, a fluorescent substancecontaining nitrogen can be obtained. This nitrogen-containingfluorescent substance is formed of a composition represented, inaccordance with the kind of raw material of oxide fluorescent substance,by M₂Si₅N₈:Z (wherein M is at least one selected from the groupconsisting of Sr, Ba and Ca; and Z is at least one activator selectedfrom the group consisting of Eu and Ce). Since this fluorescentsubstance is excellent in crystallinity and is formed of highlytransparent particles, this fluorescent substance is enabled to exhibitexcellent properties such as high luminance, high energy efficiency andhigh quantum efficiency.

The product thus obtained may contain, apart from the elements containedin M₂Si₅N₈:Z, residual impurities which were originally included in theraw materials. Examples of such residual impurities include Co, Mo, Ni,Cu and Fe. Since these impurities would become a cause for thedeterioration of emission luminance or a cause for obstructing theactivity of the activator, these impurities should be removed out of thesystem as far as possible. These impurities can be eliminated by anysuitable measures such as the employment of high purity raw material(oxide fluorescent substance) or the employment of clean experimentalequipment.

If Eu is employed as an activator for the fluorescent substance having acomposition represented by M₂Si₅N₈:Z, the fluorescent substance isenabled to absorb a first emission spectrum falling within a wavelengthregion of near-ultraviolet (NUV) ranging approximately from 370 to 410nm or a wavelength region of blue ranging approximately from 420 to 470nm. On the other hand, if Ce is employed as an activator for thefluorescent substance, the fluorescent substance is enabled to absorb afirst emission spectrum falling within a wavelength region of NUVranging approximately from 370 to 430 nm. Irrespective of the kind ofelement (Eu or Ce) to be employed, the concentration of Z shouldpreferably be confined within the range of: Z/(M+Z)=0.03−0.13 (in molarratio). When Z is included in the composition at a concentration fallingwithin this range, it is possible to obtain a nitrogen-containingfluorescent substance of high luminance which is capable of exhibitingan emission spectrum ranging from yellow to red. Thisnitrogen-containing fluorescent substance is also excellent intemperature characteristics and hence is capable of exhibiting excellentemission characteristics throughout a wide range of service temperatureof LEDs, i.e. ranging from −30° C. to 200° C.

It is now possible, through the employment of the method according tothis embodiment of the present invention, to easily manufacture anitrogen-containing fluorescent substance at a high yield. While the rawoxide fluorescent substances are capable of exhibiting green, yellow ororange light emission, the nitride fluorescent substances thus obtainedthrough the reduction/nitrification of oxide fluorescent substance areall enabled to exhibit red, orange or yellow light emission. Therefore,this nitrogen-containing fluorescent substance is advantageous in therespect that it can be coated on a light-emitting diode immediatelyafter the manufacture of this nitrogen-containing fluorescent substancewhen manufacturing a light-emitting device without necessitating themixing of the nitride fluorescent substance with another fluorescentsubstance which is capable of exhibiting a predetermined color ofemission.

In order to enhance the moisture resistance of the particles offluorescent substance thus obtained, the particles may provide with aspecific kind of surface material on a surface. For example, it ispossible to employ, as such a surface material, at least one selectedfrom the group consisting of silicone resin, epoxy resin, fluororesin,tetraethoxy silane (TEOS), silica, zinc silicate (for example, ZnO.cSiO₂(1≦c≦4)), aluminum silicate (for example, Al₂O₃.dSiO₂ (1≦d≦10)), calciumpolyphosphate, silicone oil and silicone grease. The surface of theparticles may not be completely covered with such a surface material butmay be partially exposed. Namely, as long as a surface materialcontaining any of the aforementioned materials is existed on the surfaceof particles of fluorescent substance, the effects of moistureresistance can be obtained.

The surface material can be deposited on the surface of particles offluorescent substance by using a dispersion or solution of the surfacematerial. Specifically, the surface material can be deposited on thesurface of particles of fluorescent substance in such a manner that theparticles of fluorescent substance are dipped in a dispersion orsolution of the surface material for a predetermined period of time andthen allowed to dry by heating, for instance, thereby depositing thesurface material on the surface of particles of the fluorescentsubstance. The surface material should preferably be deposited on thesurface of particles of the fluorescent substance at about 0.1-5% basedon the volume of the particles of the fluorescent substance.

FIG. 1 shows a cross-sectional view of the light-emitting deviceaccording to one embodiment of the present invention.

In the light-emitting device shown in FIG. 1, the resin stem 10 thereofcomprises lead wires 11 and 12 formed from a lead frame, and a resinportion 13 which is formed integral with the lead frame. The resinportion 13 is provided with a first recess 15 having an upper openingwhich is made larger in area than the bottom thereof. A light reflectionsurface 14 is formed on the sidewall of this recess 15.

A second recess 17 is formed at a central portion of the circular bottomsurface of the first recess 15. A light-emitting chip 16 is mounted at acentral portion of the bottom of the second recess 17 by using an Agpaste, etc. As for the light-emitting chip 16, it is possible to employone which is capable of ultraviolet light emission or one which iscapable of emitting light of the visible radiation region. Theelectrodes (not shown) of the light-emitting chip 16 are electricallyconnected, via bonding wires 19 and 20 made of Au, etc., with the leadwire 11 and the lead wire 12, respectively. The arrangement of theselead wires 11 and 12 may be variously altered. Incidentally, thereference number 18 denotes a light reflection surface, the referencenumber 21 denotes a fluorescent substance-containing resin, and thereference number 22 denotes a sealing body.

Inside the second recess 17 formed in the resin portion 13, there isdisposed a fluorescent substance layer (a fluorescentsubstance-containing resin) 21. This fluorescent substance layer 21 canbe formed by dispersing the fluorescent substance of one embodiment ofthe present invention in a resin layer formed of a silicone resin forexample at a ratio ranging from 5 to 50 wt %.

As for the light-emitting chip 16, it is also possible to employ a chipof a flip-chip type where the n-type electrode and p-type electrode areboth formed on the same surface. In this case, since the provision oflead wires is no longer required, it is possible to obviate the problemssuch as the cut-off or peeling of lead wire, or the problems originatingfrom the provision of lead wires, such as the light absorption by thelead wire, thereby making it possible to obtain a semiconductorlight-emitting device which is excellent in reliability and inluminance. Further, by using an n-type substrate for the fabrication ofthe light-emitting chip 16, the following structure can be fabricated.More specifically, an n-type electrode is formed on the rear surface ofthe n-type substrate and a p-type electrode is formed on the top surfaceof the semiconductor layer on the substrate. Then, leads are mounted soas to connect them with the n-type electrode and the p-type electrode,respectively. The n-type electrode and the p-type electrode areconnected respectively with the other lead by using wires.

As for the size of the light-emitting chip 16 and the size andconfiguration of the first recess 15 and the second recess 17, they canbe optionally modified as long as the fluorescent substance is enabledto effectively emit light. The fluorescent substance according to oneembodiment of the present invention is capable of emitting a bluishgreen-reddish light through the excitation thereof using a light havinga wavelength ranging from 360 nm to 550 nm. When the fluorescentsubstance according to one embodiment of the present invention isemployed in combination with a blue-emitting fluorescent substance and ared-emitting fluorescent substance, it is also possible to obtain awhite light.

The fluorescent substance layer made of the fluorescent substanceaccording to one embodiment of the present invention can be employed incombination with a semiconductor light-emitting element having a firstemission spectrum for the manufacture of a light-emitting device. Thisfluorescent substance is capable of shifting the wavelength of at leastpart or all of the first emission spectrum to create a second emissionspectrum formed of at least one emission band and falling within adifferent wavelength region from that of the first emission spectrum.Therefore, it is possible to obtain a light-emitting device which iscapable of emitting light of various colors apart from blue, green,yellow and red. As one example of the nitrogen-containing fluorescentsubstance according to one embodiment of the present invention, it ispossible to employ an alkaline earth metal-based nitrogen-containingsilicide fluorescent substance. This fluorescent substance correspondsto those that can be represented by the aforementioned general formula(1) wherein M is Si, Ba or Ca and Z is Eu or Ce, and is capable ofabsorbing light of a short wavelength falling within an ultraviolet-blueregion, i.e. a wavelength ranging from 250 to 550 nm and capable ofemitting light of a long wavelength falling within an orange-red region,i.e. a wavelength ranging from 580 to 780 nm.

As explained above, according to the embodiment of the presentinvention, it is possible to easily synthesize a nitrogen-containingfluorescent substance which is excellent in emission characteristics andto manufacture, through the employment of this nitrogen-containingfluorescent substance, a light-emitting device which is excellent instability and capable of constantly emitting excellent white light.

Next, the present invention will be further explained in detail withreference to specific examples.

First of all, by using SrCO₃ powder (2.4 μm in average particlediameter) as a raw material for the M component, BaCO₃ powder (2.6 μm inaverage particle diameter) as another raw material for the M component,SiO₂ powder (0.9 μm in average particle diameter), and Eu₂O₃ powder (1.1μm in average particle diameter) as a raw material for the activator Z,an oxide fluorescent substance was synthesized. Incidentally, theseSrCO₃, BaCO₃, Eu₂O₃ and SiO₂ powders were mixed together at a molarratio of: 1.84:0.12:0.04:1.00, respectively. The mixture thus obtainedwas placed in an alumina crucible and sintered in a reducingnitrogen/hydrogen mixed gas atmosphere for 3-7 hours at a temperatureranging from 1000 to 1400° C. The product obtained from this sinteringstep was examined by using an X-ray powder diffraction apparatus, thusconfirming it as having a composition of: (Sr,Ba)₂SiO₄:Eu.

The (Sr,Ba)₂SiO₄:Eu fluorescent substance thus obtained was subjected topulverization, washing with water, sieving and drying to obtain a rawmaterial (oxide fluorescent substance) for the nitrogen-containingfluorescent substance.

The oxide fluorescent substance thus pulverized was placed in a carboncrucible and sintered at a temperature of 1630° C. in a reducing mixedgas atmosphere formed through the supply of hydrogen gas and nitrogengas at a volume ratio of: 1:1. After continuing the sintering for 8hours, the product was examined by a fluorescence microscope, theproduct was confirmed as formed of a mixed fluorescent substancecontaining (Sr,Ba)₂Si₅N₈:Eu and (Sr,Ba)₂SiO₄:Eu, the volume ratiothereof being 90:10. This fluorescent substance will be hereinafterreferred to as Example 1.

Further, in addition to the aforementioned SrCO₃ powder, BaCO₃ powderand CaCO₃ powder were also prepared as raw materials for the Mcomponent. In addition to the aforementioned Eu₂O₃ powder, Ce₂O₃ powderwas also prepared as a raw material for the activator Z. By variouslychanging the composition of these raw materials as well as the sinteringconditions as shown in the following Table 1, the synthesis of thefluorescent substances of Examples 2-10 was performed according to themethod representing one embodiment of the present invention.

TABLE 1 Sintering conditions Compositions of Temp. Time AtmosphereComposition ratio No. raw materials (° C.) (h) H₂/N₂ Crucible ofproduct* 1 (Sr,Ba)₂SiO₄:Eu 1630 8 1:1 Carbon 90/10 2 (Sr,Ba)₂SiO₄:Eu1630 3 1:3 Carbon 10/90 3 (Sr,Ba)₂SiO₄:Eu 1630 2.5 1:1 Carbon 50/50 4(Sr,Ba)₂SiO₄:Eu 1630 3 1:1 Carbon 60/40 5 (Sr,Ba)₂SiO₄:Eu 1630 10 1:1SiC 70/30 6 (Ba,Ca)₂SiO₄:Eu 1650 2.5 1:3 Carbon 25/75 7 (Sr,Ba)₂SiO₄:Eu1630 10 1:1 Carbon 100/0  8 (Sr,Ba)₂SiO₄:Ce 1600 3 1:1 Carbon 10/90 9Sr₂SiO₄:Ce 1600 3 1:1 Carbon 10/90 10 Ba₂SiO₄:Ce 1600 3 1:1 Carbon 30/70*(weight of nitride fluorescent substance)/(weight of oxide fluorescentsubstance)

FIG. 2 shows an emission spectrum obtained from the excitation ofnear-ultraviolet-LED by the fluorescent substance of Example 3, and FIG.3 shows an emission spectrum obtained from the excitation of a blue-LEDby the fluorescent substance of Example 3. In FIG. 2, a region in thevicinity of 380-430 nm corresponds to the first emission spectrum. Thefluorescent substance of Example 3 was excited by a light having awavelength of approximately 380-430 nm and was enabled to emit a lightof approximately 550-780 nm (the second emission spectrum). In FIG. 3, aregion in the vicinity of 440-520 nm corresponds to the first emissionspectrum. The fluorescent substance of Example 3 was excited by lighthaving a wavelength of approximately 440-520 nm and was enabled to emitlight of approximately 560-780 nm (the second emission spectrum).

Further, FIG. 4 shows an emission spectrum obtained from the excitationof near-ultraviolet-LED by the fluorescent substance of Example 7, andFIG. 5 shows an emission spectrum obtained from the excitation ofblue-LED by the fluorescent substance of Example 7. In FIG. 4, a regionin the vicinity of 380-430 nm corresponds to the first emissionspectrum. The fluorescent substance of Example 7 was excited by lighthaving a wavelength of approximately 380-430 nm and was enabled to emita light of approximately 570-780 nm (the second emission spectrum). InFIG. 5, a region in the vicinity of 440-520 nm corresponds to the firstemission spectrum. The fluorescent substance of Example 7 was excited bylight having a wavelength of approximately 440-520 nm and was enabled toemit light of approximately 570-780 nm (the second emission spectrum).FIG. 6 shows an excitation spectrum of the fluorescent substance ofExample 7. It will be seen from FIG. 6 that the fluorescent substance ofExample 7 was capable of being excited by the first emission spectrumincluding not only an emission spectrum of the near-ultraviolet-LED(i.e. in the vicinity of 380-430 nm) but also an emission spectrum ofthe blue-LED (i.e. in the vicinity of 440-520 nm).

FIG. 7 shows an emission spectrum obtained from the excitation ofnear-ultraviolet-LED by the fluorescent substance of Example 8,indicating that the fluorescent substance of Example 8 was excited bylight having a wavelength of approximately 380-430 nm and was enabled toemit light of approximately 470-700 nm (the second emission spectrum).

Generally, if a white LED is to be manufactured by using anear-ultraviolet (NUV) LED, a blue fluorescent substance, a yellow(green) fluorescent substance and a red fluorescent substance are mixedtogether at a predetermined ratio and dispersed in a resin to obtain adispersion which is then deposited, as a fluorescent substance layer, onan NUV-LED chip, thereby manufacturing the white LED. On the other hand,if a white LED is to be manufactured by using a blue-LED, a yellow(green) fluorescent substance and a red fluorescent substance are mixedtogether at a predetermined ratio and then deposited likewise, as afluorescent substance layer, on a blue-LED chip, thereby manufacturingthe white LED.

As explained above, when the sintering conditions are optimized, it ispossible, through the employment of the method representing oneembodiment of the present invention, to obtain a mixed fluorescentsubstance comprising an oxide fluorescent substance and a nitridefluorescent substance. If a blue-LED is to be employed, since thesefluorescent substances to be used comprising a yellow (green)fluorescent substance and a red fluorescent substance, the mixedfluorescent substance is mixed with a resin and coated, as it is, on theblue-LED chip to manufacture a white LED. If an NUV-LED is to beemployed, only a blue fluorescent substance is mixed with the mixedfluorescent substance.

When the sintering conditions are optimized, it is possible, through theemployment of the fluorescent substance representing one embodiment ofthe present invention, to form a fluorescent substance layer by using adispersion of only the fluorescent substance in a resin withoutnecessitating the process of mixing it with other fluorescent substanceswhich are capable of emitting different colors. Therefore, the presentinvention is advantageous in the respect that the manufacturing processof a white LED can be simplified.

According to the embodiment of the present invention, it is possible toprovide a method for effectively manufacturing a fluorescent substancewhich is capable of exhibiting useful white light-emittingcharacteristics. Further, according to the embodiment of the presentinvention, it is possible to provide a fluorescent substance whose colortone can be easily adjusted in combination with a light-emitting diodein the manufacture of a white light-emitting device. Furthermore,according to the embodiment of the present invention, it is possible toprovide a light-emitting device which is capable of emitting white lightwhich is quite suitable as an illumination for display application orfor medical application.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A nitrogen-containing fluorescent substance manufactured by themethod comprising: accommodating an oxide fluorescent substancecomprising two or more metal elements in a receptacle made of a materialcomprising carbon; and sintering the oxide fluorescent substanceaccommodated in the receptacle made of a material comprising carbon in amixed gas atmosphere comprising nitrogen gas.
 2. A nitrogen-containingfluorescent substance manufactured by the method comprising: sinteringan oxide fluorescent substance represented by the following generalformula (1) in a mixed gas atmosphere containing nitrogen gas, therebyconverting at least part of the oxide fluorescent substance into anitrogen-containing fluorescent substance represented by the followinggeneral formula (2):M₂SiO₄:Z  (1)M₂Si₅N₈:Z  (2) wherein M is at least one selected from the groupconsisting of Sr, Ba and Ca; and Z is at least one activator selectedfrom the group consisting of Eu and Ce.
 3. A light-emitting devicecomprising: a light-emitting element having a first emission spectrum;and a fluorescent layer comprising a nitrogen-containing fluorescentsubstance of claim 1, the nitrogen-containing fluorescent substanceshifting the wavelength of at least part of the first emission spectrum,thereby exhibiting a second emission spectrum formed of at least oneemission band and falling within a different wavelength region from thatof the first emission spectrum.
 4. A light-emitting device comprising: alight-emitting element having a first emission spectrum; and afluorescent layer comprising a nitrogen-containing fluorescent substanceof claim 2, the nitrogen-containing fluorescent substance shifting thewavelength of at least part of the first emission spectrum, therebyexhibiting a second emission spectrum formed of at least one emissionband and falling within a different wavelength region from that of thefirst emission spectrum.
 5. The nitrogen-containing fluorescentsubstance of claim 2, wherein the oxide fluorescent substance of formula(1) has a particle size ranging from 5 to 20 μm.
 6. Thenitrogen-containing fluorescent substance of claim 2, wherein componentZ of formula (2) is present in a molar ratio that satisfies:Z/(M+Z)=0.03−0.13.
 7. The nitrogen-containing fluorescent substance ofclaim 2, wherein the sintering occurs at a temperature of at least1,600° C.
 8. The nitrogen-containing fluorescent substance of claim 7,wherein the temperature is from 1,600 to 1,700° C.
 9. Thenitrogen-containing fluorescent substance of claim 2, wherein thenitrogen containing gas further comprises hydrogen.
 10. Thenitrogen-containing fluorescent substance of claim 9, wherein hydrogenand nitrogen are present in a ratio ranging from 10:90 to 70:30.
 11. Thenitrogen-containing fluorescent substance of claim 2, wherein Z informula (2) represents Eu.
 12. The nitrogen-containing fluorescentsubstance of claim 11, wherein the oxide fluorescent compound of formula(2) absorbs a first emission spectrum at a wavelength ranging from 370to 410 nm.
 13. The nitrogen-containing fluorescent substance of claim 2,wherein Z in formula (2) represents Ce.
 14. The nitrogen-containingfluorescent substance of claim 13, wherein the oxide fluorescentcompound of formula (2) absorbs a first emission spectrum at awavelength ranging from 370 to 430 nm.
 15. The nitrogen-containingfluorescent substance of claim 1, wherein sintering occurs at atemperature ranging of at least 1,600° C.
 16. The nitrogen-containingfluorescent substance of claim 1, wherein the nitrogen containing gasfurther comprises hydrogen.
 17. The nitrogen-containing fluorescentsubstance of claim 7, wherein hydrogen and nitrogen are present in aratio ranging from 10:90 to 70:30.